The defections came in the outskirts of capital Damascus and the port city of Latakia, where large explosions were heard near the presidential palace, the Syrian Media Center reported, according to al-Arabiya.

Meanwhile, the official news agency SANA reported that one of the military units stationed off the coast of Latakia thwarted an attempt by an armed terrorist group "trying to infiltrate from the sea," quoting an unnamed military source, according to al-Arabiya.

According to activist Sema Nassar, fighting began as "officers and soldiers of a military base near the presidential palace ... deserted with their weapons," al-Arabiya reported.

The team in Homs is part of an advance team of 15 U.N. monitors in Syria who are trying to salvage a peace plan brokered by special envoy Kofi Annan that aims to end the country's 13-month-old crisis. Under the plan, a cease-fire is supposed to lead to talks between President Bashar Assad and the opposition on a political solution to the conflict that has killed more than 9,000 people.

But the plan has been deeply troubled since the truce began on April 12. The regime has kept up its attacks on opposition strongholds, while rebel fighters continue to ambush security forces. Defying a major truce provision, the Syrian military has failed to withdraw tanks and soldiers from the streets.

Most analysts say the plan has little chance of succeeding, though it could temporarily bring down the level of daily violence.